Hello Ajinkya,

In order to be eligible to answer JEE advanced, you first have to answer JEE mains and get the cutoff score to be eligible to answer JEE advanced. For that, you will have to answer JEE mains as well Advanced in the same academic year. If you are planning on answering JEE mains now and if you are qualified to answer JEE advanced and plan on answering it after 2 years, your score wouldn't be valid and hence you will not be allowed to directly answer JEE advanced. So, my advice is plan your preparations and answer both the exams in the same year.

According to the eligibility conditions given by IITs to appear for JEE Advanced, one must clear 12th in the year in which he (she) is appearing for JEE or the last year i,e., If you clear your 12th in 2020 then you will be eligible to appear for JEE Advanced in 2020 and 2021 only.

After 2021, you will be eligible to appear for JEE Main in 2022. After that you will not be eligible to appear for JEE Main and advanced both.